This invention relates to a cutting tool suitable for severing bundles of cabled strands. It is particularly useful in cutting what is known as "communications" cable, and it will be described in that frame of reference, although it may be used in severing other objects. Communications cable comprises a bundle or group of bundles of very small diameter electrical conductors, each strand of which carries a coating of insulating material. Such cables may contain as many as several hundred filaments in a cable only a few inches in diameter. They are highly resistant to severing.
Until the present invention, there seems to have been no manually-operable commercially-available tool that was capable of cutting cables of this type without causing damage to at least some of the conductors. Saws have a tearing effect; knives and chisels smash the insulation and distort the conducting elements; shears are as destructive as chisels. Previously-known tools for doing this work are bulky and ineffective, since they are difficult to operate without repeated manual adjustment as each cut is made, and the stress imposed by the shearing action flattens the cable and strips the insulating coat.
One of the tools previously used resembles a pair of pliers in which one of the jaws is a knife and the other jaw serves as an anvil. A major objection to this type of tool is its very limited capacity to cut large-diameter cable. Unless the knife is quite thick, its edge will curl or chip instead of cutting. But the thicker the blade, the greater must be the displacement of the metal in the cable being cut, the greater the force required to make the cut, and the greater the tendency to flatten and distort the cable.
Tools having a shearing action are likely to draw the very fine strands of the cable into the zone between the blades of a shear-type tool, thus wedging the blades apart and jamming the jaws, while at the same time stripping insulation from some of the conductors. The result is a ragged cut instead of a smooth one, and the distortion of the cable at the point where it is cut makes it difficult or impossible to fit the severed ends neatly into clamps or fittings of rigid metal.
The problem presents a vicious circle: The blades in a shear-type cutter simply must be thick, not only to resist nicking and curling of their cutting edges, but also to counteract the tendency to spread apart, with resultant outward flaring, when making a cut. Yet the thickness required greatly increases the energy needed to drive them through the cable being cut, and this cannot be remedied in the usual way--namely, by lengthening the handles to add leverage, because the tool itself must often operate in very confined quarters--e.g., in a manhole, where the total clearance available may be not much more than the shoulder width of a sturdy man. There is no room for long handles. This is an unavoidable limitation, because the manhole must accommodate not only the cable sections, but also various accessories for the system as a whole.
While hydraulically or pneumatically driven cutting devices are known which can cut very thick cable, they are in general bulky and expensive, and require use of pneumatic or hydraulic lines and pumps.